CD may be referring to papers by Farrar that appeared in the Transactions of the Ethnological Society of London and the Anthropological Review (Farrar 1864a, 1864b, and 1864c). CD referred to Farrar 1864b in Descent 1: 65 n.

Summary

Thanks for book on language [Chapters on language (1865)], which he hopes to read soon if his weak health permits.